Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2002-01-04
2003-11-25
Black, Thomas G. (Department: 3663)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S220000, C340S545500, C244S003200, C244S079000, C079S003000, C073S078000
Reexamination Certificate
active
06654685
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to aircraft navigation systems and, more particularly, to an apparatus and method for aircraft navigation that utilizes a blended architecture consisting of a global positioning system (GPS) and micro-electromechanical sensors (MEMS) for the primary navigation system and a laser gyroscope system for the secondary navigation system.
BACKGROUND OF THE INVENTION
An aircraft navigation system is the source of data for many critical avionics functions, such as the primary flight control system, the flight deck displays, and guidance, control, and stabilization systems, including automatic landing systems. The navigation system measures a variety of parameters defining the state of the aircraft, such as attitude, heading, angular rates, acceleration, track angle, flight path angle, ground speed and position, and provides the data to the avionics systems for display and for use in the control of the aircraft's flight.
Commercial aircraft have generally relied upon inertial navigation. Inertial navigation requires that the navigation system be initialized at a starting position and provide autonomous and continuous measurements based on that reference. As such, inertial navigation systems are particularly useful for over-water navigation where it is more difficult to obtain ground references for the measurements. Most inertial navigation systems, however, are expensive and are subject to increases in position error, commonly called “drift,” over time.
More particularly, most modem commercial aircraft are equipped with traditional or, less commonly, fault-tolerant Air Data Inertial Reference Units (ADIRU) to perform stand-alone inertial navigation and provide the necessary air data to the avionics systems. To ensure that navigational data is continuously provided during a flight, aircraft generally have more than one, typically three, traditional ADIRUs operating in parallel in a redundant arrangement, called a triplex configuration. Such traditional ADIRUs are used in the majority of large commercial aircraft. In this regard, those aircraft having Category
3
B automatic landing capability require three ADIRUs, while the other navigational requirements can be minimally met with two ADIRUs. Alternatively, the most modern commercial aircraft may have a single, fault-tolerant ADIRU configuration that is constructed to be equivalent to three separate traditional ADIRUs. The single fault-tolerant ADIRU is constructed such that if any one component fails, the ADIRU remains operational, since the same ADIRU includes redundant components. In fact, the fault-tolerant ADIRU is generally constructed to remain operational even if any two components fail.
Each traditional ADIRU has three navigation-grade ring laser gyroscopes and three accelerometers. Therefore, a triplex configuration of the traditional ADIRUs has a total of nine navigation-grade ring laser gyroscopes and nine accelerometers. Each fault-tolerant ADIRU, on the other hand, has six navigation-grade ring laser gyroscopes and six accelerometers. The navigation-grade ring laser gyroscopes and accelerometers provide inertial navigation for the aircraft with a low amount of drift, typically less than 0.01 degree/hour, but they are expensive. All ADIRUs, traditional and fault-tolerant, require that the inertial measurements be obtained with great precision and that subsequent processing of those measurements maintain that precision. Thus, ADIRU processors generally have a complex and proprietary sensor interface to provide the precise timing, measurements and specialized features that are necessary. In addition, the processors and interfaces must generally be manufactured or provided by the same company that provided the sensors to ensure compatibility among the components of the ADIRU. ADIRUs are available from various vendors including the Honeywell HG2050 (traditional ADIRU) and HG2060 (fault-tolerant ADIRU) and the Litton (Northrop Grumman) LTN-101 (traditional ADIRU).
An aircraft equipped with a fault-tolerant ADIRU also carries a Secondary Attitude Air data Reference Unit (SAARU), which is a backup to the ADIRU in the rare event that the ADIRU malfunctions. This architecture is called a Fault-Tolerant Air Data Inertial Reference System (FT-ADIRS). The components of the SAARU are intentionally dissimilar to the ADIRU to preclude common failures in both units. That is, the SAARU generally will not include ring laser gyroscopes if the ADIRU includes ring laser gyroscopes. The SAARU may have four attitude-grade fiber optic gyroscopes. The fiber optic gyroscopes provide the necessary dissimilar design, but suffer from a higher amount of drift than the laser gyroscopes of the ADIRU with the drift generally being several degrees/hour. In addition, fiber optic gyroscopes are also costly. Like the laser gyroscopes of the ADIRU, the fiber optic gyroscope configuration of the SAARU requires its own processors, power supplies, input/output modules and proprietary interface to process signals, which also increases the cost of the SAARU. Furthermore, the SAARU is not fault-tolerant, so it must be fully functional before aircraft operation to ensure the availability of this backup unit.
By way of example,
FIG. 1
depicts a conventional FT-ADIRS architecture, located in the forward electrical/electronics bay of a Boeing
777
aircraft, with a single, fault-tolerant ADIRU
12
. The ADIRU
12
has six ring laser gyroscopes and six accelerometers designated generally as
14
and four processors
16
(P
1
-P
4
) to process the signals from the gyroscopes and accelerometers
14
. The processors
16
communicate with other avionics systems via the flight control buses, which generally include a right flight control bus
26
, a center flight control bus
28
and a left flight control bus
30
. The three flight control buses conform to ARINC standard
629
and are high-speed, two-way data buses that are shared by all subscribing ARINC
629
input/output (I/O) terminals attached to them. The I/O modules in the fault-tolerant ADIRU serve to receive air data sensor inputs and to transmit the entire suite of inertial and air data state signals to user avionics systems, such as flight instruments, flight management, automatic pilot controls and primary flight controls. Since signals may be transmitted both to and from the ADIRU
12
via the right
26
and left
30
flight control bus, transceivers
20
,
24
are generally disposed between the respective input/output modules
18
and the right
26
and left
30
flight control bus. In contrast, since signals are generally received by the ADIRU
12
from the center flight control bus
28
, a receiver
22
is generally disposed between the respective input/output modules
18
and the center flight control bus
28
. To provide the desired redundancy, the ADIRU
12
generally includes multiple redundant processors
16
, at least two input/output modules
18
associated with each flight control bus
26
,
28
,
30
and at least two transceivers or receivers
20
,
22
,
24
in communication with the respective flight control bus.
FIG. 1
also shows the backup SAARU
32
with components that are dissimilar to the components of the ADIRU
12
. The SAARU
32
has four fiber optic gyroscopes
34
and two processors
36
(PY, PZ) to process the signals from the gyroscopes
34
. The SAARU
32
also includes multiple input/output modules
38
, one of which is associated with each flight control bus
26
,
28
,
30
. The respective input/output modules
38
are, in turn, connected to the right
26
and left
30
flight control bus by respective receivers
40
,
44
and to the center flight control bus
28
by a transceiver
42
.
The flight control buses are also connected to the left Aircraft Information Management System (AIMS)
52
and the right AIMS
50
. The left AIMS
52
is generally connected to the left flight control bus
30
by a transceiver
64
and to the center
28
and right
26
flight control bus by a receiver
60
,
62
. Conversely, the right AIMS
50
is
Alston & Bird LLP
Black Thomas G.
The Boeing Company
To Tuan L
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